1. Technical Field
The present invention relates to self-photoinitiating multifunctional acrylate compositions. More particularly, the present invention relates to liquid oligomeric multifunctional acrylate compositions having tertiary amine groups bound as part of the polymer structure. The compositions of the present invention cure upon exposure to active radiation such as UV light in the absence of an added photoinitiator. Films made from the crosslinked oligomers of the invention are used as protective or decorative coatings on various substrates. The oligomers can be added to other resins used in adhesives or composites.
2. Background of Invention
Multifunctional acrylates, methacrylate and other unsaturated monomers are widely used in coatings, adhesives, sealants, elastomers, crosslinked films, foundry sand binders and composite structures. These monomers may be crosslinked by free radical chain mechanism, which may require any of a number of free radical generating species such as peroxides, hydroperoxides or azo compounds, for example, which may decompose to form radicals when heated, or at ambient temperature in the presence of amines or transition metal promoters.
Another means of initiating reaction, currently not as widespread but gaining in popularity, is the use of UV radiation to decompose photoinitiators to free radicals. This method offers extremely rapid processing potential for a number of applications, as the transformation from a liquid reactive composition to a crosslinked solid is essentially instantaneous upon exposure to UV radiation.
A drawback to both means of effecting free radical reaction is that the decomposition of initiator or photoinitiator can produce low molecular weight fragments that may volatilize during or after the manufacturing process, creating issues with regard to worker, consumer and environmental safety. For instance, these low molecular weight fragments tend to be readily absorbed through skin which can cause adverse health effects.
Another drawback is that free radical reactions of acrylates are typically inhibited by oxygen, i.e. the presence of oxygen prevents complete reaction.
These limitations have been addressed in several key approaches. The challenge of fugitive emissions during manufacturing processes or subsequent leaching due to photoinitiator fragments has been attacked by creating acrylate monomers/oligomers with xe2x80x9cbuilt-inxe2x80x9d photoinitiators. This may be accomplished by starting with a compound which is known to function as a photoinitiator (or a suitable derivative) and either functionalizing it with an appropriate unsaturated group, i.e. acrylate or methacrylate, so as to produce a new compound which functions as both monomer/oligomer and photoinitiator, or by xe2x80x9cgraftingxe2x80x9d onto a preformed oligomer/polymer in order to produce a higher molecular weight photoinitiator.
Regardless of the effectiveness of these methods, they add additional manufacturing procedures and costs.
Also, with these approaches, low functionality may be detrimental to reactivity and final properties, and catalyst or initiator may be required to effect crosslinking.
A more recent and effective solution is described in U.S. Pat. Nos. 5,945,489 and 6,025,410 to Moy et al and assigned to Ashland, Inc., the assignee of the present application. Such approach involves reacting multifunctional acrylates with acetoacetates via Michael Addition in ratios which yield uncrosslinked, acrylate-functional resins. These resins crosslink upon exposure to an appropriate UV source in the absence of added photoinitiators.
Oxygen inhibition of free radical acrylate reactions can be eliminated by inerting, i.e. exclusion of oxygen by inert gases, nitrogen being the most common. While this is an obvious solution, it is generally most appropriate for research or for specialty purposes since it is oftentimes impractical or prohibitively expensive for large-scale industrial applications. Another option, frequently more attractive from a cost perspective, is the use of amine synergists, tertiary amines which enhance surface cure. A wide variety are available, but even well-known simple compounds such as common ethanolamine derivatives may function as effective synergists. However, as these are generally somewhat lower molecular weight compounds which may be present at 5 to as much as 15% (by weight) of a formulation in addition to added photoinitiators, fugitive emissions or subsequent leaching remain a potential problem.
Accordingly, considerable room still exists for improvement, such as addressing problems associated with added low molecular weight photoinitiators and synergists.
The present invention relates to significantly reducing, if not eliminating, problems associated with added low molecular weight photoinitiators and synergists by incorporating appropriate functional groups for these purposes into multifunctional acrylates/acrylate functional oligomers.
In particular, the present invention is directed to a self-photoinitiating liquid oligomeric composition having tertiary amine groups comprising a Michael-type Addition reaction product of:
A) uncrosslinked Michael addition reaction product of a multifunctional acrylate acceptor and a Michael Donor wherein the amount of the Michael Donor is not sufficient to effect crosslinking; and
B) a primary and/or secondary amine.
The multifunctional acrylate is employed in excess of the Michael Donor and typically the equivalent ratio of the multifunctional acrylate to Michael Donor is about  greater than 1:1 to about 13.2:1. The equivalent ratio of unreacted acrylate double bands in A):B) is typically about 100:1 to about 2:1.
The present invention also relates to crosslinked products obtained by subjecting the above disclosed self-photoinitiating liquid oligomeric compositions to actinic light such as UV radiation.
The present invention also relates to curing the above disclosed self-photoinitiating liquid oligomeric compositions by exposing the compositions to actinic light.
Another aspect of the present invention relates to a method which comprises applying the above disclosed self-photoinitiating liquid oligomeric composition to a substrate and then exposing the composition to actinic light.
A still further aspect of the present invention relates to the product obtained by the above disclosed method.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.
Among the multiacrylates used to make the oligomers of this invention are diacrylates, triacrylates and tetracrylates.
Examples of diacrylates are: 
Examples of triacrylates are: 
Examples of suitable Michael Donors include active methylene compounds such as acetoacetates, cyanoacetates, 2,4-pentanediones, malonate esters, acetoacetanilides, and acetoacetamides. The Michael Donors have functionality of at least two and typically from about 2 to about 8.
Examples of acetoacetates having a functionality of two are: 
Examples of acetoacetates having a functionality of four are: 
Examples of acetoacetates having a functionality of six are: 
An example of an acetoacetate having a functionality of eight is: 
According to the present invention, the multifunctional acrylate must be employed in amounts in excess of the equivalent reaction amounts with respect to the Michael Donor. Typically, the equivalent ratio of the multifunctional acrylate to acetoacetate is at least 1:1 to about 13.2:1.
By way of illustrations, the following preferred equivalent ratios are provided:
1) diacrylate acceptor: Michael Donor of
 greater than 1:1 where donor functionality=2
xe2x89xa74.5:1 where donor functionality=4
xe2x89xa74.5:1 where donor functionality=6
xe2x89xa74.5:1 where donor functionality=8
2) triacrylate acceptor: Michael donor of
xe2x89xa72.25 where donor functionality=2
xe2x89xa76.4:1 where donor functionality=4
xe2x89xa77.8:1 where donor functionality=6
xe2x89xa77.4:1 where donor functionality=8
3) tetraacrylate acceptor: Michael Donor of
xe2x89xa76.6:1 where donor functionality=2
xe2x89xa712.3:1 where donor functionality=4
xe2x89xa713.2:1 where donor functionality=6
xe2x89xa712.7:1 where donor functionality=8.
The equivalent ratio of the unreacted acrylate double bands in above Michael reaction product to the secondary amine is typically about 100:1 to about 2:1, more typically about 50:1 to about 4:1, and preferably about 10:1 to about 6:1.
Typical primary amines are aliphatic amines such as mono- and poly-amines and including alkyl amines, hydroxyalkyl amines and cyclic amines. Examples of same suitable primary amines are ethanolamine, 1-amino-2-propanol, aminopropyl triethoxysilane; difunctional primary amines such as methyl-1,6-hexanediamine, 2-methyl-1,5-pentanediamine, 1,3-diamino pentane; Jeffamine(copyright) T-403 (a trifunctional amine); 3-aminopropyl trimethoxysilane, ethylamine, ethylene diamine, benzylamine, n-butylamine, sec-butylamine, 2-amino-1-butanol, 3-amino-1,2-propanediol, 3-(dimethylamino) propylamine, 3-(diethylamino) propylamine, propylamine, diaminopropane, diaminobutane, hexylamine, heptylamine, 1,6-hexanediamine, 1,2-diaminocyclohexane, 1,4-diamino cyclohexane, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and isophorone diamine.
Typically, secondary amines are alkyl amines, hydroxyalkyl amines and cyclic amines. Suitable alkyl amines are dimethylamine, diethylamine and dipropylamine, and dibutylamine. Suitable hydroxyalkyl amines are diethanolamine and N-methylethanolamine. Suitable cyclic amines are piperidine, piperazine and morpholine.
The secondary amines are preferred.
The Michael addition reactions can be catalyzed by a strong base; diazabicycloundecene (DBU) is sufficiently strong and readily soluble in the monomer mixtures. Other cyclic amidines, for example diazabicyclo-nonene (DBN) and guanidines are also suitable for catalyzing this reaction.
The compositions of the present invention can be cured without added photoinitiators by exposure to actinic light and especially to UV radiation.
The liquid oligomer compositions of the present invention, since they are liquids, can readily be applied to various substrates using coating technologies such as roll or spray prior to the actinic light cure.
The following non-limiting examples are presented to further illustrate the present invention. In the following examples, all parts are by weight unless otherwise indicated. In addition, all references mentioned herein are specifically incorporated by reference.